Transport and Concentrations of Selected Herbicides and Nitrate
in the Sangamon River, Illinois, April 1991 - March 1992

Abstract

The Sangamon River, located in east-central Illinois, drains some of
the most intensively used agricultural land in the Midwest. Effects of agricultural
practices in the drainage basin on stream-water quality were investigated
by collecting surface-water samples from April 1991 through March 1992 at
Monticello, Illinois. Samples were analyzed for concentrations of selected
herbicides and nitrate. Total load was calculated and compared to estimated
application totals of each compound in the drainage basin above Monticello.

During the study period, 1,607 pounds of atrazine were transported by
the river; this mass represents 1.4 percent of the total annual application
of 113,700 pounds. The river transported 669 pounds of cyanazine--a mass
equal to 1.6 percent of the total annual application of 41,900 pounds. About
353 pounds of alachlor were transported by the river (0.31 percent of the
112,300 pounds applied). About 12,100 tons of nitrogen fertilizer were applied,
and 3,393 tons of nitrate as nitrogen were transported by the river (28
percent of the total amount applied). However, other natural and human-derived
sources of nitrate could have contributed to this total load.

The timing of chemical application and the quantity of rainfall and runoff
after herbicide application affected the concentrations. Herbicide concentrations
were highest in early spring during storms immediately following application.
Peak concentrations for atrazine, cyanazine, and alachlor occurred in May;
these concentrations were 21, 16, and 8.8 micrograms per liter, respectively.
Nitrate concentrations were at or above the U.S. Environmental Protection
Agency's maximum contaminant level of 10 milligrams per liter from the beginning
of the study until June 11, 1991. Nitrate concentrations then remained less
than the maximum contaminant level until November 1991.